It is known that imaging layers suitable for coating on a substrate are prepared by dispersing a solution of an imageable polyacetylenic compound in a binder material and coating such dispersions on a polyester film base. In normal use, the unexposed portion of the film is not removed and is subject to development by prolonged exposure to visible light. For example, several weeks of exposure to the lighting intensity of a normal office environment or daylight can cause the background or unexposed portions of the imageable layer to turn blue. Such exposure to visible light causes degradation of the transmitted pattern by diminishing contrast between the imaged and background, or non-imaged, portions of the film.
Because the crystal size of commercially available, normally crystalline polyacetylenic compounds is often relatively large and of varying dimension and since for imageable coatings, a microcrystalline size between about 0.01 and about 5 micrometers is desirable, the commercial polyacetylenic compound is usually dissolved in a solvent from which it can be subsequently recrystallized as fine discrete crystals of more uniform microcrystalline size. An ester such as ethyl acetate is generally selected for forming the solution of the polyacetylenic compound which is subsequently dispersed as crystals in an aqueous binder solution suitable for coating on a film base. However, films prepared by this method lack the desired resistance to visible light radiation.
Accordingly, it is an object of this invention to overcome the above disadvantages by a process which is economical and commercially feasible.
Another object of this invention is to prepare an imageable polyacetylenic dispersion of improved stability with respect to visible radiation.
Another object is to provide an imageable polyacetylenic dispersion of increased sensitivity to ionizing radiation.
These and other objects of this invention will become apparent from the following description and disclosure.